The disclosure of Japanese Patent Application No. 2000-079952 filed on Mar. 22, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an electrode catalyst solution for a fuel cell, and a production method for the electrode catalyst solution. More particularly, the invention relates to an electrode catalyst solution for use for forming an electrode of a polymer electrolyte fuel cell, and a production method for the electrode catalyst solution.
2. Description of the Related Art
Electrode catalyst solutions for fuel cells for being applied or coated to electrolyte films have been proposed (e.g., in WO94/25993). Such a solution is prepared by using 2.6 mg of perfluorinated sulfonic acid NAFION solution (5 wt % of NAFION (registered trademark)) polymer, 50 wt % of isopropyl alcohol, 25 wt % of methanol, and 20 wt % of water), 390 mg of 1-methoxy 2-propanol, 2 ml of isopropanol, and 487.9 mg of a catalyst having 20 wt % of platinum supported on VULCAN (registered trademark) carbon (produced by Precious Metals Corporation).
In this electrode catalyst solution, however, since the catalyst-loaded carbon is dispersed in a solution containing great amounts of quick drying solvents, heat generation or a catalyst sink ring often occurs at the time of dispersion in many cases. Therefore, the operability in the preparation of the solution or the mass-productivity thereof decreases, or the catalyst electrode formed therefrom has degraded performance. As a countermeasure against the heat generation at the time of dispersion of the catalyst-loaded carbon, a technique of dispersing the catalyst-loaded carbon in water is possible. In this case, however, the dry shrinkage of the solution after being printed onto an electrolyte film or the like is great, so that cracks and the like are formed in the catalyst layer. Thus, it is difficult to form a uniform catalyst layer.
Accordingly, it is an object of the invention to provide an electrode catalyst solution that forms a uniform catalyst layer and forms a high-performance catalyst electrode. It is another object to improve the operability in the formation of an electrode catalyst.
To achieve the aforementioned objects, an electrode catalyst solution for use for forming an electrode of a polymer electrolyte fuel cell in accordance with the invention is prepared by (a) mixing a water and a solvent which, when alone, has a higher boiling point than the water, and which, in an aqueous solution, boils together with the water at a predetermined temperature, and (b) dispersing a catalyst-loaded carbon powder in the obtained solution.
Therefore, it becomes possible to prevent ignition of the catalyst-loaded carbon powder caused by heat generated at the time of dispersing the carbon powder. Furthermore, since the azeotropic solvent boils together with water, the solvent evaporates together with water at the time of forming a catalyst electrode, and does not remain as a residue. As a result, high performance of the catalyst electrode formed by using the solution can be maintained.